Teams searching for a missing Malaysian airliner are planning for the first time to send an unmanned submarine into the depths of the Indian Ocean to look for wreckage, an Australian official leading the multi-nation search said Monday.
The deployment of the submersible drone opens a new phase in the five-week search, one focusing on a pitch-black, silt-covered patch of the ocean floor. The drone moves at walking speed, and searching with it will be painstaking. But it allows investigators to follow up on their best lead to date: deep-sea acoustic signals that have come from the Boeing 777's black box.
The submersible drone, known as the Bluefin-21, will use sonar to provide search crews with a three-dimensional map of the Indian Ocean floor, an area so unexplored that it is practically "new to man," said Angus Houston, the Australian official in charge of the search. The Bluefin-21 will likely begin its mission Monday evening.
Thirty-eight days into the search for Malaysia Airlines Flight 370, which vanished with 239 passengers and crew on board, there have been no confirmed sightings of debris. The best hint of the plane's location comes from four acoustic signals - potential black-box transmissions - that were detected by an Australian naval vessel equipped with specialized listening equipment. The last transmission, though, came six days ago, and the aircraft black-box batteries are already well past their 30-day shelf life. The batteries by now could have died, Houston said.
"I would caution against raising hopes that the deployment of the autonomous underwater vehicle will result in the detection of aircraft wreckage," Houston said. "It may not. However, this is the best lead we have.
"We've got to find wreckage before we can finally say we've solved this mystery."
The Bluefin-21 - 16 feet long, yellow, shaped like a submarine - is already on board the Australian vessel, the Ocean Shield, operating roughly 1,050 miles northwest of Perth. For more than a week, the Ocean Shield has been dragging a towed pinger locator through the water to listen for possible pings from Flight 370's black box.
Separately, Houston said Monday, the Ocean Shield also came across an oil slick about 3 1/2 miles downwind from the area where it picked up the signals. Though the oil slick could be unrelated to the plane, about half a gallon has been sampled for analysis - a process that will take several days, Houston said.
The Ocean Shield doesn't have the capability to use the towed pinger locator - connected to miles of cables - and the Bluefin-21 at the same time. The four pings were detected in a loose oval about 20 to 25 miles apart; that translates into an underwater search zone of some 500 square miles. Search officials had been hoping that additional detections could help narrow the ocean floor area where the submersible will scan for evidence of the plane. The U.S. Navy said the submersible will need anywhere from six weeks to two months to scan the underwater search area.
Australian Prime Minister Tony Abbott said last week that authorities were "confident" that the deep-sea pings were coming from the missing plane's flight data recorder and cockpit voice recorder.
The underwater operation will be a slow one, moving in 24-hour cycles. The submersible will spend 20 hours at a time underwater: two hours to make the dive, 16 hours scanning the depths, and two more hours for the ascent. Crew members on the Ocean Shield will then take four hours to download the data. The Bluefin-21 does not transmit information about what it is seeing in real time.
The Bluefin-21 will be operating in depths approaching its technological limits, but U.S. naval officials say they believe the drone will be effective.
Houston said the submersible would begin its search "in the most likely spot" of the wreckage, but he gave no additional specifics about that location. He added that a search for any debris bobbing on the ocean surface could wind down later this week after consultation with the other countries involved.
"The chances of any floating material being recovered have greatly diminished," Houston said.
For now, the disappearance of Flight 370 - a red-eye from Kuala Lumpur bound for Beijing - remains a dismaying mystery. Malaysian authorities say the flight was steered off course deliberately, though they have not indicated a culprit or provided any suggestion of a motive.
Investigators determined based on communication between the plane and a satellite that Flight 370 almost certainly crashed in the southern Indian Ocean, presumably after running out of fuel. The search field has narrowed significantly in recent weeks, but 12 aircraft and 15 ships were still scouring an area of more than 18,000 square miles on Monday.
Countries involved in the search, including the United States, are running up "big costs," Houston said, and he warned that the hunt may continue much longer. The only comparable operation, he said, occurred after Air France Flight 447 vanished in 2009 over the Atlantic Ocean. The aircraft's black box was not recovered until two years later. And the ocean where Malaysia Airlines Flight 370 is believed to have crashed is nearly a mile deeper.
"I think that gives you some idea of how challenging this should be," Houston said. "And that's why I say we've got to be realistic about this. It may be very difficult to find something, and you don't know how good any lead is until you get your eyes on the wreckage."